Turbocharger apparatus

ABSTRACT

A variable turbocharger apparatus includes a housing, a compressor mounted for rotation in the housing, a turbine mounted for rotation in the housing, a first inlet for enabling air to be conducted to the compressor, an outlet for enabling air from the compressor to be conducted to an engine, a second inlet for enabling exhaust gases from the engine to be conducted to the turbine in order to rotate the turbine, a chamber which surrounds the turbine and which receives the exhaust gases from the second inlet before the exhaust gases are conducted to the turbine, and a bearing assembly for permitting the rotation of the turbine. Fixed vanes are mounted in the chamber which are for accurately directing exhaust gases on to the turbine. A piston is slidable and is positioned between the vanes and the turbine. Control means is connected to the piston and is for controlling the sliding movement of the piston, the piston having an end which is nearest the bearing assembly and which defines a gap, the size of the gap being variable in dependence upon the sliding of the piston under the control of the control means, the size of the gap being effective to control the amount of the exhaust gases that act on the turbine thereby controlling the speed of rotation of the turbine and thereby the amount of air conducted by the compressor through the outlet to the engine. The end of the piston is such that it has a flange which extends radially outwardly and which is provided with slots for receiving the vanes.

FIELD OF THE INVENTION

This invention relates to turbocharger apparatus and, more especially,this invention relates to variable turbocharger apparatus.

BACKGROUND OF THE INVENTION

Variable turbocharger apparatus is known comprising a housing, acompressor mounted for rotation in the housing, a turbine mounted forrotation in the housing, a first inlet for enabling air to be conductedto the compressor, an outlet for enabling air from the compressor to beconducted to an engine, a second inlet for enabling exhaust gases fromthe engine to be conducted to the turbine in order to rotate theturbine, a chamber which extends around the turbine and which receivesthe exhaust gases from the second inlet before the exhaust gases areconducted to the turbine, a bearing assembly for permitting the rotationof the turbine, and a heat shield for shielding the bearing assemblyfrom the exhaust gases. This known type of variable turbochargerapparatus may require the use of a non-standard bearing assembly, whichincreases manufacturing costs. Also, gas leakage can be a problem.

It is an aim of the present invention to obviate or reduce the abovementioned problems.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides variable turbochargerapparatus comprising a housing, a compressor mounted for rotation in thehousing, a turbine mounted for rotation in the housing, a first inletfor enabling air to be conducted to the compressor, an outlet forenabling air from the compressor to be conducted to an engine, a secondinlet for enabling exhaust gases from the engine to be conducted to theturbine in order to rotate the turbine, a chamber which surrounds theturbine and which receives the exhaust gases from the second inletbefore the exhaust gases are conducted to the turbine, and a bearingassembly for permitting the rotation of the turbine, the variableturbocharger apparatus comprising fixed vanes which are mounted in thechamber and which are for accurately directing exhaust gases on to theturbine, a piston which is slidable and which is positioned between thevanes and the turbine, and control means which is connected to thepiston and which is for controlling the sliding movement of the piston,the piston having an end which is nearest the bearing assembly and whichdefines a gap, the size of the gap being variable in dependence upon thesliding of the piston under the control of the control means, the sizeof the gap being effective to control the amount of the exhaust gasesthat act on the turbine thereby controlling the speed of rotation of theturbine and thereby the amount of air conducted by the compressorthrough the outlet to the engine, and the end of the piston being suchthat it has a flange which extends radially outwardly and which isprovided with slots for receiving the vanes.

The variable turbocharger apparatus of the present invention is able touse a standard bearing assembly, and it is also able to substantiallyeliminate gas leakage in the region of the vanes.

The flange on the end of the piston forms a control ring that operatesover the vanes. By using the flange, the exhaust gases are guided moreaccurately through the vanes onto the turbine. Thus the flange enablesthe performance of the variable turbocharger apparatus to be enhanced.Pressure on the back face of the flange helps to keep the piston in aclosed position, so that a smaller sized control means may be used. Gasleakage through the slots where the vanes are located is not a problemwith the variable turbocharger apparatus of the present inventionbecause gas pressure is the same both sides of the flange. During use ofthe variable turbocharger apparatus, if a carbon deposit builds up onthe vanes, then this is cleaned off as the flange of the piston movesbackwards and forwards over the vanes. Gas leakage is prevented when thepiston is in its closed position. When the piston is in its closedposition, this is the most vulnerable time for gas leakage. However,with the variable turbocharger apparatus of the present invention, allthe gases are guided accurately through the vanes, the heat shield andthe flange as required.

The variable turbocharger apparatus may include a heat shield forshielding the bearing assembly from heat from the exhaust gases. Theheat shield may be a ring-shaped heat shield. Alternatively, the heatshield may be a disc shaped heat shield having an outer ring portion, aninner wall portion, and an aperture through the inner wall portion.

The fixed vanes may be mounted on the heat shield.

The variable turbocharger apparatus of the present invention may includean insert located in the housing, and may be one in which the vanes aremounted on the insert.

The insert may be a removable insert which is removable from thehousing, the removable insert being such that it facilitates assembly ofthe variable turbocharger apparatus.

The removable insert may be held in position by a spring. The spring maybe such that it forms a seal for preventing gas leakage from the chamberwhich surrounds the turbine. The spring may be advantageous formanufacture and assembly of the variable turbocharger apparatus in thatit reduces tolerance requirements.

If desired, the insert may be a non-removable insert which is notremovable from the housing.

The variable turbocharger apparatus may be one in which the pistonpasses through a bore in the insert.

The variable turbocharger apparatus may be one in which the fixed vanesare mounted on a part of the housing which is adjacent the bearingassembly and which defines an exit from a chamber.

Advantageously, the piston has a first abutment for forming a sealagainst a mating surface thereby to prevent loss of the exhaust gasesbetween the abutment and the mating surface. The mating surface may be amating surface on a part of the housing. Alternatively, the matingsurface may be a mating surface on an insert in a part of a housing.

The variable turbocharger apparatus may be one in which the piston has asecond abutment for engaging against the end of the vanes, therebysetting the gap when the piston is in its closed position.

The variable turbocharger apparatus may include a sealing ring forforming an auxiliary seal for preventing loss of any of the exhaustgases that pass between the first abutment and the mating surface.

The control means may include a fork member which is connected to thepiston on two opposed sides. Alternatively, the control means mayinclude a U-shaped member which is connected to the piston on a face ofthe piston.

The variable turbocharger apparatus may be one in which the slots areopen slots which extend inwardly from a periphery of the flange, orclosed slots in the flange.

The control means will be an electronic control means which operates aspart of an engine management control system. The control system may alsouse an air or oil operated actuator control means in conjunction withthe engine management system.

The variable turbocharger may be one in which the chamber is a volute.Various types of chamber may be employed, for example of various crosssectional shapes.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described solely by way ofexample and with reference to the accompanying drawings in which:

FIG. 1 is a section through first variable turbocharger apparatus with apiston in a closed position;

FIG. 2 is a section like FIG. 1 but through second variable turbochargerapparatus and with a piston in a fully open position;

FIG. 3 is a section like FIG. 1 but through third variable turbochargerapparatus and with a piston in a closed position:

FIG. 4 is a section like FIG. 1 but through fourth variable turbochargerapparatus and with a piston in a closed position;

FIG. 5 is a section like FIG. 1 but through fifth variable turbochargerapparatus and with a piston in a closed position;

FIG. 6 is a side view of the first turbocharger apparatus shown in FIG.1 and illustrates control means having a fork member which is connectedto the piston on two opposed sides of the piston;

FIG. 7 is a section through the heat shield shown in the first variableturbocharger apparatus of FIG. 1;

FIG. 8 is an end view of the heat shield shown in FIG. 7;

FIG. 9 is the section through a piston which is like the piston shown inFIG. 5 but which is for use with control means of the type shown inFIGS. 1, 2 and 6;

FIG. 10 is an end view of a flange part of the piston shown in FIG. 9,the flange having slots for vanes;

FIG. 11 is an end view of a control ring fixed to the end of a piston,the control ring having slots extending inwardly from a periphery of thecontrol ring;

FIG. 12 is an end view of a control ring where the slots are completelywithin the control ring;

FIG. 13 is a side view of the piston shown in FIGS. 1 and 2, andillustrates how the control ring shown in FIGS. 11 and 12 may be fittedto the piston;

FIG. 14 is a section through sixth variable turbocharger apparatus ofthe present invention;

FIG. 15 is a section through seventh variable turbocharger apparatus ofthe present invention;

FIG. 16 is a section through eighth variable turbocharger apparatus ofthe present invention;

FIG. 17 is a section through ninth variable turbocharger apparatus ofthe present invention;

FIG. 18 is a side view of the piston used in the variable turbochargerapparatus shown in FIGS. 14-16; and

FIG. 19 is an end view of the piston as shown in FIG. 18.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring to FIG. 1, there is shown variable turbocharger apparatus 2comprising a housing 4 a compressor 6 mounted for rotation in thehousing 4, and a turbine 8 which is also mounted for rotation in thehousing 4. The variable turbocharger apparatus 2 also comprises a firstinlet 10 for enabling air to be conducted to the compressor 6, and anoutlet 12 for enabling air from the compressor 6 to be conducted to anengine (not shown).

The variable turbocharger apparatus 2 has a second inlet 14 for enablingexhaust gases from the engine to be conducted to the turbine 8 in orderto rotate the turbine 8. A chamber 16 extends around the turbine 8 andreceives the exhaust gases from the second inlet 14 before the exhaustgases are conducted to the turbine 8.

A bearing assembly 18 permits the rotation of the turbine 8. A heatshield 20 is provided for shielding the bearing assembly 18 from heatfrom the exhaust gases.

The variable turbocharger apparatus 2 comprises fixed vanes 22 which aremounted in the chamber 16 and which are for accurately directing theexhaust gases on to the turbine 8. A piston 24 is positioned between thefixed vanes 22 and the turbine. The piston 24 is a slideable piston.Control means 26 control the sliding movement of the piston 24.

The piston 24 has an end 28 which is adjacent the heat shield 20. Thisend 28 is spaced apart from the heat shield by a gap 30. FIG. 1 showsthe piston 24 in a closed position in which the gap 30 is at itssmallest condition. The size of the gap 30 is variable in dependenceupon the sliding of the piston 24. The sliding of the piston 24 is underthe general control of the control means 26. The size of the gap 30 iseffective to control the amount of the exhaust gases that acts on theturbine 8, thereby accurately controlling the speed of rotation of theturbine 8 and thereby the amount of air conducted by the compressorthrough the outlet 12 to the engine.

As shown in FIG. 1, the variable turbocharger apparatus 2 also comprisesa shaft 32 on which the turbine 8 and the compressor 6 are mounted. Thecompressor 6 is secured to a reduced diameter end portion 34 of theshaft 32 by a nut 36 which screws on to a screw threaded portion 38 onthe end portion 34 of the shaft 32.

The turbine 8 has a central body portion 40 and vanes 42. The compressor6 has a central body portion 44 and vanes 46.

Compressed air from the compressor 6 passes along a diffuser passage 48into a chamber 50 in the form of a volute as shown. The chamber 16feeding the exhaust gases to the turbine 8 is also in the form of avolute as shown.

Bolts 52 bearing on washers 54 secure a back plate 56 to a part of thehousing 4 that is for the compressor 6. Bolts 58 go Into the bearingassembly 18 to hold the back plate 56 in position.

The bearing assembly 18 has an oil intake 60 for providing oil for thebearing assembly 18. Also provided is an oil drain 62.

Bolts 64 act on a clamping plate 66 to clamp the bearing assembly 18 tothe part of the housing 4 that is for the turbine 8.

The piston 24 slides against an insert 68 as shown. The insert can bemade of a corrosion resistance material depending upon the material usedfor the housing 4. The housing 4 can basically be regarded as being athree part housing comprising a turbine housing 4A, a compressor housing4B, and a bearing housing 4C.

The control means 26 has an air intake 70 for controlling an actuatormember 72. A diaphragm (not shown) in the actuator member 72 is actedupon by the air. The air intake is controlled by an electronic controldevice (not shown). Movement of the diaphragm causes movement of an arm74. The arm 74 pivots a rod 76 (see FIG. 6). The rod 76 as best shown inFIG. 6 is connected to a fork device 78 having a pair of arms 80, 82each arm 80, 82 has a locator member 84. Each locator member 84 locatesin a recess 86 as shown in FIG. 1.

As can be seen from FIG. 1, the fixed vanes 22 are mounted on the heatshield 20. In an alternative embodiment of the invention, the fixedvanes 22 may be mounted on a part of the housing 4 which is opposite theheat shield 20 and which defines an exit from the chamber 16.

The piston 24 has an abutment 88 for forming a seal against a matingsurface 90, thereby to prevent loss of the exhaust gases between theabutment 88 and the mating surface 90. As shown in FIG. 1, the matingsurface 90 is formed as a part of the housing 4.

The provision of the abutment 88 and the mating surface 90 may besufficient to prevent the loss of the exhaust gases between the abutment88 and the mating surface 90. As an extra precaution against the loss ofthe exhaust gases, a seal 94 is provided. In FIG. 1, the seal 94 isprovided in an insert 96 in a part of the housing 4. The seal 94 is inthe form of a sealing ring and it thus acts to form an auxiliary sealfor preventing loss of any of the exhaust gases that might pass betweenthe abutment 88 and the mating surface 90.

The end 28 of the piston 24 has a flange 91. The flange 91 extendsradially outwardly as shown. The flange 91 is provided with slots (notshown in FIG. 1) for receiving the vanes 22.

The heat shield 20 shown in FIG. 1 is a disk shaped heat shield havingan outer ring portion 93 and an inner wall portion 95. The inner wallportion 95 has a aperture 97 through which the turbine 8 passes.

FIG. 2 is a section through second variable turbocharger apparatus 99.The second variable turbocharger apparatus 99 is similar to the variableturbocharger apparatus 2 shown in FIG. 1 and similar parts have beengiven the same reference numerals for ease of comparison andunderstanding. In FIG. 2, it will be seen that the heat shield 20 doesnot have the inner wall portion 95. In FIG. 2 it will also be seen thatthe piston 24 is shown in its open position, rather than in its closedposition as shown in FIG. 1.

FIG. 3 shows third variable turbocharger apparatus 101. FIG. 4 showsfourth variable turbocharger apparatus 103. FIG. 5 shows fifth variableturbocharger apparatus 105. The variable turbocharger apparatus 101shown in FIG. 3, 103 shown in FIGS. 4 and 105 shown in FIG. 5 is similarto the variable turbocharger apparatus 2 shown in FIGS. 1 and 99 shownin FIG. 2. Similar parts have again been given the same referencenumerals for ease of comparison and understanding.

In FIG. 3 the variable turbocharger apparatus 101 is operated by controlmeans 27 which is similar to the control means 26. The control means 27is shaped as shown in FIGS. 3, 4 and 5 and it connects by three arms 29to a piston 31 as shown in FIG. 3, or to a piston 33 as shown in FIG. 4,or to a piston 35 as shown in FIG. 5. The arms 29 connect to a shaft 37which connects to the actuator member 72.

In FIG. 3, the vanes 22 are cast as part of the heat shield 20. In FIG.4, the vanes 22 are case onto an insert 107. The piston 33 works againstthe insert 107 as shown in FIG. 4.

In FIG. 5, the flange 91 is provided with a return portion 109 which isreceived in a groove 111 as shown.

In FIG. 1, the flange 91 is shown in the closed position, with thepiston 24 having been moved by the control means 26. The travel of thepiston 24 towards its closed position is arrested by a stop portion 113on the piston 24. FIG. 2 shows the piston 24 in the open position. FIG.3 shows the piston 31 in the closed position with the closing movementof the piston 31 having been stopped when a stop portion 115 of thepiston 31 engages the ends of the vanes 22. In FIG. 4, a stop portion117 on the piston 33 engages a flange 119 on the insert 107 in order tostop the inward travel of the piston 33. In FIG. 5, a stop portion 121engages the ends of the vanes 22 in order to stop the inward travel ofthe piston 35. FIG. 4 also shows a design with no heat shield, and withthe vanes cast on the insert 107. In order to keep the bearing assemblycool, a water jacket 129 is provided with a water passageway 131.

FIG. 6 is an end view of the turbocharger apparatus 2 shown in FIG. 1and illustrates in more detail the location of the actuator member 72.

FIGS. 7 and 8 show the heat shield 20. The heat shield 20 has fixedvanes 22. The heat shield 20 also has an outer ring portion 93 which issimilar in shape to the heat shield 20 shown in FIG. 2. However the heatshield 20 also has the inner wall portion 95 which provides additionalheat shielding facilities for the bearing assembly 18.

FIGS. 9 and 10 show a piston 104 which is like the piston 35 shown inFIG. 5 but which uses the control means 26 shown in FIG. 1. Although notshown in FIG. 9, the piston 104 may be provided with a pin to stoprotation of the piston 104 during use of the variable turbochargerapparatus. FIG. 9 also shows the piston 104 provided with a groove 86 toconnect to the fork device 78 shown in FIG. 6. FIG. 10 is a end view ofthe piston flange, and shows the slots for the vanes.

FIG. 11 shows a design for a piston flange 121. Slots 123 are cut intothe flange 121 from the outer periphery of the flange 121 as shown. Thisdesign may be an economically way to produce the flange 121. The flange121 and be formed as a separate ring which can secured to the remainderof the piston 24 by a weld 125 as shown in FIG. 13. Alternatively, theweld 125 can be a peen or a screw. FIG. 12 shows how slots 127 mayalternatively be completely formed in the flange 121. Again the flange121 shown in FIG. 12 may be formed as a separate ring for attachment tothe remainder of the piston 24 as shown in FIG. 13.

Referring now to FIGS. 14-18, similar parts as in previous Figures havebeen given the same reference numerals for ease of comparison andunderstanding. In FIG. 14, there is shown variable turbochargerapparatus 150 having an insert 152 on which the fixed vanes 22 aremounted. The insert 152 is removable from the turbine housing 4. A discspring 154 is used to push the insert 152 to the left as shown in FIG.14 and over and against the bearing assembly 18. The disc spring 154 isalso used as a seal for preventing gas leakage.

As also shown in FIG. 14, an abutment in the form of a stop ring 156 isemployed to set the start gap 30 over the turbine wheel. The stop ring156 abuts against a small lip 158 on the piston 24. The stop ring 156may be spot welded, crimped or otherwise held in position. When the stopring 156 is set against the lip 158, the stop ring 156 may then preventall of the gas leakage from passing through the piston 24 when thepiston 24 is in the closed position and thus when the piston 24 ispushed against the insert 152.

The variable turbocharger 150 shown in FIG. 14 allows the piston 24, theinsert 152 and the stop ring 156 to be assembled as an assembly into theturbine housing 4A. The disc spring 154 also acts as a seal to preventgas leakage passing the volute area of the variable turbochargerapparatus 150, so that all the gases are used on the turbine wheel andthereby performance is improved.

FIG. 15 shows variable turbocharger apparatus 160 which is like thevariable turbocharger apparatus 150 shown in FIG. 14. In the variableturbocharger apparatus 160, the bearing assembly 18 has a heat shield 20for helping to prevent heat build up in the bearing area. Thisparticular design may be employed in variable turbocharger apparatusthat is designed to run hotter than usual. FIG. 15 also shows the use ofa seal 162 in the insert 152. The seal 162 is for preventing gas leakagewhen the piston 24 is in its open position.

As shown in both FIGS. 14 and 15, the stop ring 156 prevents all gasleakage passing the piston 24 when the piston 24 is in its closedposition, since this is the most difficult part of the operating rangeof the turbocharger apparatus for being able to achieve goodperformance.

FIG. 16 shows variable turbocharger apparatus 164 which is like thevariable turbocharger apparatus 150 and 160. As shown in FIG. 16, thevariable turbocharger apparatus 164 has an insert 152 with the fixedvanes 22. However this insert 152 has screw threads 166 which allow theinsert 152 to be screwed into the turbine housing 4. The screw threads166 provide a sealing function, whilst at the same time allowing theinsert 152 to be located in position in the turbine housing 4A. The useof the screw threads 166 also allows the assembly of the insert 152, thepiston 24 and the stop ring 156 to be screwed into the turbine housing4A as one single unit.

Referring now to FIG. 17, there is shown variable turbocharger apparatus168 having an insert 152, vanes 22, a piston 24 and a flange 170. Thepiston 24 also has a stop ring 172 which is designed as shown with agroove 174. The stop ring 172 is used to allow a fork member 78 to beconnected to the stop ring 172, and to move the piston 24 and the stopring 172 in the variable turbocharger apparatus 168. The stop ring 172sets the gap 30 when the piston 24 is in its closed position. When theactuator 72 moves the control rod 74, this in turn moves a fork 78 thatcontrols the movement of the piston 24. The variable turbochargerapparatus 168 shown in FIG. 17 enables hot gases to be prevented fromworking on the fork member 78 and its associated parts by having alonger piston 24. As shown in FIG. 17, this longer piston 24 operates toshield the fork member 78 from the hot gases.

FIG. 17 also shows that the turbine housing 4 is machined to provide anair gap 178. The air gap 178 is positioned between the bearing assembly18 and the turbine housing 4A. With this arrangement, a heat shield isnot required because the turbine housing 4A also acts as a heat shield.The design of the variable turbocharger apparatus 168 shown in FIG. 17also allows for the piston 24, the insert 152 and the stop ring 172 tobe fitted into the turbine housing 4A as an assembly. FIG. 17 furthershows the use of clamps 179 for clamping the turbine housing 4A to thebearing assembly 18.

FIGS. 18 and 19 show the piston 24 used in the variable turbochargerapparatus shown in FIGS. 14, 15 and 16. As can be seen from FIG. 18,there are arms 180 that hold the control rod 182 that connects to theactuator that moves the piston 24. Also shown in FIG. 18 is the step 158for the stop ring 156 so that when the stop ring 156 is set against thestep 158 and appropriately fixed in position, for example by welding orcrimping, gas leakage is stopped when the piston 24 is in its closedposition. Also this piston 24 may be stamped or formed as a single unitso the piston and flange are made as one part.

FIG. 19 best illustrates how the slots 184 for the vanes 22 are openended slots. With variable turbocharger apparatus of the invention witha flange on the end of the piston, and with the vanes going through theslots in the flange, the performance of the variable turbochargerapparatus may be greatly increased. Also, the flange keeps the vanesclean when moving along the vanes. The vanes and the slots preventrotation of the piston. Where the variable turbocharger apparatus of thepresent invention employs an insert, then insert with the vanes isutilised for guiding gases to the turbine wheel. The insert allows forthe piston to work inside the bore of the insert between the vanes andturbine wheel. The use of a removable insert which is removable from theturbine housing allows for assembly of the piston into the turbinehousing of the variable turbocharger apparatus. The variableturbocharger apparatus may be unique in its use of a spring to hold theinsert and prevent gas leakage, in its use of an insert that is screwedinto the turbine housing and that allows the piston assembly to beassembled as a unit in the turbine housing, in the use of an insert thatis removable in order to allow part of a piston assembly to seal againstthe insert to prevent gas leakage, and in the use of an insert that isremovable and which allows part of a piston assembly to locate on a sideof the insert so as to set the gap of the end of the piston over theturbine wheel.

The different variations of the variable turbocharger apparatus of thepresent invention and shown in the accompanying drawings are able towork efficiently and to be manufactured economically. The gap 30 is ableto be varied by the sliding piston 24. The flange on the end of thepiston forms a control ring that slides over the vanes. By using theflange, the exhaust gases are guided more accurately through the vanesonto the turbine. Thus, the performance of the variable turbochargerapparatus is enhanced. Pressure on the back face of the flange helps tokeep the piston in a closed position, so that a smaller sized controlmeans may be used. Gas leakage through the slots where the vanes arelocated is not a problem with the variable turbocharger apparatus of thepresent invention because gas pressure is the same both sides of thecontrol ring. During use of the variable turbocharger apparatus, if acarbon deposit builds up on the vanes, then this is cleaned off as theflange of the piston moves backwards and forwards over the vanes, withthe vanes passing through the slots in the flange. Gas leakage isprevented when the piston is in its closed position. When the piston isin its closed position, this is the most vulnerable time for gasleakage. However, with the variable turbocharger apparatus of thepresent invention, all the gases are guided accurately through thevanes, the heat shield and the flange in order to work on the turbine asrequired.

It is to be appreciated that the embodiments of the invention describedabove with reference to the accompanying drawings have been given by wayof example only and that modifications may be effected. Thus, forexample, the shape of the chambers 16 and 50 may be varied. Also, thenumber of vanes may vary, and the sealing rings may be used or not usedas may be desired.

1. Variable turbocharger apparatus comprising a housing, a compressormounted for rotation in the housing, a turbine mounted for rotation inthe housing, a first inlet for enabling air to be conducted to thecompressor, an outlet for enabling air from the compressor to beconducted to an engine, a second inlet for enabling exhaust gases fromthe engine to be conducted to the turbine in order to rotate theturbine, a chamber which surrounds the turbine and which receives theexhaust gases from the second inlet before the exhaust gases areconducted to the turbine, and a bearing assembly for permitting therotation of the turbine, the variable turbocharger apparatus comprisingfixed vanes which are mounted in the chamber and which are foraccurately directing exhaust gases on to the turbine, a piston which isslidable and which is positioned between the vanes and the turbine, andcontrol means which is connected to the piston and which is forcontrolling the sliding movement of the piston, the piston having an endwhich is nearest the bearing assembly and which defines a gap, the sizeof the gap being variable in dependence upon the sliding of the pistonunder the control of the control means, the size of the gap beingeffective to control the amount of the exhaust gases that act on theturbine thereby controlling the speed of rotation of the turbine andthereby the amount of air conducted by the compressor through the outletto the engine, and the end of the piston being such that it has a flangewhich extends radially outwardly and which is provided with slots forreceiving the vanes.
 2. Variable turbocharger apparatus according toclaim 1 in which the vanes are mounted on a part of the housing which isadjacent the bearing assembly and which defines an exit from a chamber.3. Variable turbocharger apparatus according to claim 1 in which thecontrol means includes a fork member, which is connected to the pistonon two opposed sides.
 4. Variable turbocharger apparatus according toclaim 1 in which the control means includes a U-shaped member which isconnected to a face of the piston.
 5. Variable turbocharger apparatusaccording to claim 1 in which the slots are open slots which extendinwardly from the periphery of the flange, or closed slots in theflange.
 6. Variable turbocharger apparatus according to claim 1 in whichthe control means is an electronic control means which operates as partof an engine management control system.
 7. Variable turbochargerapparatus according to claim 1 in which the chamber is a volute. 8.Variable turbocharger apparatus according to claim 1 and including aheat shield for shielding the bearing assembly from heat from theexhaust gases.
 9. Variable turbocharger apparatus according to claim 8in which the heat shield is a ring-shaped heat shield.
 10. Variableturbocharger apparatus according to claim 8 in which the heat shield isa disc shaped heat shield having an outer ring portion, an inner wallportion, and an aperture through the inner wall portion.
 11. Variableturbocharger apparatus according to claim 8 in which the vanes aremounted on the heat shield.
 12. Variable turbocharger apparatusaccording to claim 1 in which the piston has a first abutment forforming a seal against a mating surface thereby to prevent loss of theexhaust gases between the abutment and the mating surface.
 13. Variableturbocharger apparatus according to claim 12 in which the mating surfaceis a mating surface on a part of the housing.
 14. Variable turbochargerapparatus according to claim 12 in which the mating surface is a matingsurface on an insert in a part of the housing.
 15. Variable turbochargerapparatus according to claim 12 in which the piston has a secondabutment for engaging against the end of the vanes, thereby setting thegap when the piston is in its closed position.
 16. Variable turbochargerapparatus according to claim 12 including a sealing ring for forming anauxiliary seal for preventing loss of any of the exhaust gases that passbetween the first abutment and the mating surface.
 17. Variableturbocharger apparatus according to claim 1 and including an insertlocated in the housing, and in which the vanes are mounted on theinsert.
 18. Variable turbocharger apparatus according to claim 17 inwhich the insert is a non-removable insert which is not removable fromthe housing.
 19. Variable turbocharger apparatus according to claim 17in which the insert is a removable insert which is removable from thehousing, the removable insert being such that it facilitates assembly ofthe variable turbocharger apparatus.
 20. Variable turbocharger apparatusaccording to claim 19 in which the piston passes through a bore in theinsert.
 21. Variable turbocharger apparatus according to claim 19 inwhich the insert is held in position by a spring.
 22. Variableturbocharger apparatus according to claim 21 in which the spring is suchthat it forms a seal for preventing gas leakage from the chamber whichsurrounds the turbine.
 23. Variable turbocharger apparatus comprising ahousing, a compressor mounted for rotation in the housing, a turbinemounted for rotation in the housing, an insert located in the housing,the insert being a removable insert which is removable from the housing,the removable insert being such that it facilitates assembly of thevariable turbocharger apparatus, and the turbocharger apparatusincluding a spring for holding the insert in position, a first inlet forenabling air to be conducted to the compressor, an outlet for enablingair from the compressor to be conducted to an engine, a second inlet forenabling exhaust gases from the engine to be conducted to the turbine inorder to rotate the turbine, a chamber which surrounds the turbine andwhich receives the exhaust gases from the second inlet before theexhaust gases are conducted to the turbine, and a bearing assembly forpermitting the rotation of the turbine, the variable turbochargerapparatus comprising fixed vanes which are mounted in the chamber andwhich are for accurately directing exhaust gases on to the turbine, apiston which is slidable and which is positioned between the vanes andthe turbine, and control means which is connected to the piston andwhich is for controlling the sliding movement of the piston, the pistonhaving an end which is nearest the bearing assembly and which defines agap, the size of the gap being variable in dependence upon the slidingof the piston under the control of the control means, and the size ofthe gap being effective to control the amount of the exhaust gases thatact on the turbine thereby controlling the speed of rotation of theturbine and thereby the amount of air conducted by the compressorthrough the outlet to the engine.
 24. Variable turbocharger apparatusaccording to claim 23 in which the spring is such that it forms a sealfor preventing gas leakage from the chamber which surrounds the turbine.